The present invention relates generally to wall repair compounds such as joint compounds, spackling compounds, and the like used to repair imperfections in walls or fill joints between adjacent wallboard panels. More particularly, the present invention relates to such a wall repair compound that includes an additive which reduces the quantity of airborne dust generated when the hardened compound is sanded.
Interior walls of residential and commercial buildings are often constructed using gypsum wallboard panels, often referred to simply as xe2x80x9cwallboardxe2x80x9d or xe2x80x9cdrywall.xe2x80x9d The wallboard panels are attached to studs using nails or other fasteners, and the joints between adjacent wallboard panels are filled using a specially formulated adhesive composition called joint compound to conceal the joints. The procedure for concealing the joint between adjacent wallboards, and thereby producing a smooth seamless wall surface, typically includes applying soft wet joint compound within the joint or seam formed by the abutting edges of adjacent wallboard panels using a trowel or the like. A fiberglass, cloth, or paper reinforcing tape material is then embedded within the wet joint compound, and the compound is allowed to harden. After the joint compound has hardened, a second layer of joint compound is applied over the joint and tape to completely fill the joint and provide a smooth surface. This layer is also allowed to harden. Upon hardening, the joint compound is sanded smooth to eliminate surface irregularities. Paint or a wall covering, such as wall paper, can then be applied over the joint compound so that the joint and the drywall compound are imperceptible under the paint or wall covering. The same joint compound can also be used to conceal defects caused by the nails or screws used to affix the wallboard panels to the studs, or to repair other imperfections in the wallboard panels, so as to impart a continuously smooth appearance to the wall surface.
Various drywall joint compounds are known for concealing joints between adjacent wallboard panels. Conventional joint compounds typically include a filler material and a binder. Conventional fillers are calcium carbonate and calcium sulfate dihydrate (gypsum), which are used in xe2x80x9cready mixedxe2x80x9d joint compounds, and calcium sulfate hemihydrate (CaSO4-xc2xd H2O; also referred to as plaster of Paris or calcined gypsum), which is used in xe2x80x9csetting typexe2x80x9d joint compounds. Ready mixed joint compounds, which are also referred to as pre-mixed or drying type joint compounds, are pre-mixed with water during manufacturing and require little or no addition of water at the job site. Such joint compounds harden when the water evaporates and the compound dries. Setting type joint compounds, on the other hand, harden upon being mixed with water, thereby causing dihydrate crystals to form and interlock. Setting type joint compounds are therefore typically supplied to the job site in the form of a dry powder to which the user then adds a sufficient amount of water to give the compound a suitable consistency.
The Koltisko, Jr. et al. U.S. Pat. No. 4,972,013 provides an example of a ready-mixed (wet) joint compound including a filler, binder, thickener, non-leveling agent, and water. The McInnis U.S. Pat. No. 5,277,712 provides an example of a setting (dry mix-type) joint compound including a fine plaster material, such as stucco, a material which imparts internal strength and workability to the joint compound, such as methyl cellulose, and a material for retaining water, such as perlite. Additional examples of joint compounds are provided in the Brown U.S. Pat. No. 4,294,622; the Mudd U.S. Pat. No. 4,370,167; the Williams U.S. Pat. No. 4,454,267; the Struss et al. U.S. Pat. No. 4,686,253; the Attard et al. U.S. Pat. No. 5,336,318; and the Patent U.S. Pat. No. 5,779,786.
A spackling compound is disclosed in the Deer et al. U.S. Pat. No. 4,391,648. While joint compound and spackling compound do many of the same things and are both smeared onto walls to hide flaws, spackling compound is generally lighter, dries more quickly, sands more easily, and is more expensive than joint compound. For simplicity, joint compound, drywall joint compound, and like expressions are used throughout this specification to refer to wall repair compounds generally, including joint compound and spackling compound.
Sanding hardened joint compound can be accomplished using conventional techniques including power sanders, abrasive screens, or manual sanders which consist simply of a supporting block and a piece of abrasive paper mounted on the block. Sanding the joint compound, however, produces a large quantity of an extremely fine powder which tends to become suspended in air for a long period of time. The airborne particles settle on everything in the vicinity of the sanding site and usually require several cleanings before they can all be collected, thereby making cleanup a time consuming and tedious process. The particles may also present a serious health hazard to the worker.
The airborne particles are highly pervasive and can enter the nose, lungs, eyes and even the pores of the skin. Results from a study conducted by the National Institute for Occupational Safety and Health found that dust levels in 9 out of 10 test samples taken at test sites where workers were finishing drywall with joint compound were higher than the limits set by OSHA. The report also said that the dust may not be safe even when it falls within the recommended limits. In addition, the study found that several dust samples contained silica and kaolin, a material found in clay, which have been found to cause permanent lung damage. The report recommended the use of local exhaust ventilation, wet finishing techniques, and personal protective equipment to reduce the hazard.
In an effort to reduce the dust generation and cleanup problems associated with the sanding of conventional joint compounds, various attempts have been made to develop specialized dustless drywall sanders. The Matechuk U.S. Pat. No. 4,782,632, for example, discloses a drywall sander including a sanding head designed to minimize the release of dust and further discloses attaching a vacuum cleaner to the sanding head to collect the dust. The Krumholz U.S. Pat. No. 4,955,748 discloses a dustless drywall finisher which uses a wet sponge to prevent the formation of airborne dust.
Dust remains a problem, however, when conventional power sanders or hand sanders are used to sand conventional joint compounds. A need therefore exists for a joint compound that can be sanded using conventional sanders without producing a large quantity of fine particles capable of becoming suspended in air. It would also be desirable to provide an additive that could be mixed with commercially available joint compounds to inhibit the formation of airborne particles during the sanding procedure without otherwise interfering with the properties of the joint compound.
The present invention provides a wall repair compound, such as a joint compound or spackling compound which, when sanded, generates a lower lever of airborne particles than conventional joint compounds. More specifically, the present invention provides a wall repair compound which includes a dust reducing additive. Generally, the wall repair or joint compound includes a sufficient amount of the dust reducing additive so that when the joint compound is tested as described in this specification, it generates a lower quantity of airborne dust than the joint compound would produce if it did not contain the dust reducing additive.
The dust reducing additive can be pre-mixed into the wet joint compound prior to application or applied as a coating to the hardened joint compound after application. Generally, the dust reducing additive reduces the quantity of airborne dust particles having a size of less than or equal to 10 microns to less than 50% of the quantity that would be generated without the additive. In certain embodiments, the quantity of airborne dust particles is reduced by at least 75% compared to a mixture without the additive. Most preferably, the level of airborne dust is reduced by more than 90%. In one embodiment, the quantity of airborne particles generated by sanding the hardened joint compound of the present invention was less than 50 mg/m3 and, in certain other embodiments, less than about 15 mg/M3. The quantity of airborne particles generated by sanding the hardened joint compound is preferably less than 5 mg/m3.
It is desirable that the dust reducing additive serve to suppress the formation of airborne particles without significantly interfering with the desired characteristics of the joint compound. Suitable dust reducing additives include oils, such as mineral oils, vegetable oils and animal oils, surfactants, oleoresinous mixtures, pitch, solvents, paraffins, waxes, including natural and synthetic wax, glycols, and other petroleum derivatives. Other materials which do not fit within the above categories may also effectively reduce the quantity of dust generated by a joint compound.
The joint compound formulations include a conventional filler material and a binder material, such as a resin. The joint compound can also include a surfactant, which may or may not serve to suppress airborne dust formation, and a thickening agent. Prior to hardening, the joint compound preferably includes a sufficient amount of water to form a mud-like spreadable material which can be applied to the wall surface. The present invention further provides an additive which can be admixed with conventional joint compounds to reduce the quantity of dust generated during sanding. The dust reducing additive can be used with both drying type (i.e. ready mixed) or setting type joint compounds.
The present invention also provides a method of reducing the quantity of airborne dust generated by sanding a fully hardened joint compound which includes mixing a sufficient quantity of a dust reducing additive with the joint compound prior to applying the joint compound to a wall surface.
It is also desirable that the present invention provide a joint compound having good plasticity, water retention, cohesiveness, viscosity stability, resistance to cracking, sandability, minimal shrinkage, good paint adherence, light weight, low cost, good hardening properties, and other properties comparable to those offered by conventional joint compounds.
These and other features and advantages of the invention will be apparent to those skilled in the art when considered in view of the following detailed description.
FIG. 1 is a perspective view of the testing enclosure used to measure the quantity of airborne dust generated by sanding the wall repair compounds of the present invention.
According to the present invention, there are provided compositions suitable for filling and repairing cracks, holes, or other imperfections in a wall surface, such as the joints between adjacent wallboard panels. The compositions of the present invention include a dust reducing additive combined with conventional wall repair compound materials including a filler and a binder to form a low dust wall repair compound. Dust reducing additive refers to any ingredient capable of preventing, minimizing, suppressing, reducing, or inhibiting the formation of particles capable of becoming airborne. The expressions xe2x80x9cairborne particlesxe2x80x9d or xe2x80x9cairborne dust particlesxe2x80x9d refer to fine particles generated during the sanding or abrading of the compound which are capable of being carried by or through the air. Wall repair compound refers generally to compositions useful for filling and repairing cracks, holes, and other imperfections in surfaces such as drywall, wood, plaster, and masonry. Wall repair compounds include interior finishing and patch compounds such as joint compound, spackling compound, wood fillers, plasters, stucco, and the like. The joint compound can also include a thickener, and other materials found in conventional joint compounds.
Any conventional filler material can be used in the present invention. Suitable fillers include calcium carbonate (CaCO3) and calcium sulfate dihydrate (CaSO4-2H2O commonly referred to as gypsum) for ready mixed type joint compounds, and calcium sulfate hemihydrate (CaSO4-xc2xd H2O) for setting type joint compounds. The joint compound can also include one or more secondary fillers such as glass micro bubbles, mica, perlite, talc, limestone, pyrophyllite, silica, and diatomaceous earth. The filler generally comprises from about 25% to about 95% of the weight of the joint compound based on the total wet weight of the formulation (i.e. including water). More preferably, the filler comprises from about 55% to about 75% of the total wet weight, and most preferably, from about 60% to about 70%.
Another ingredient usually present in joint compounds is a binder or resin. Suitable binders include polyvinyl acetate, polyvinyl alcohol, ethylene vinyl acetate co-polymer, vinylacrylic co-polymer, styrenebutadiene, polyacrylamide, other acrylic polymers, other latex emulsions, natural and synthetic starch, and casein. These binders can be used alone or in combination with one another. The amount of binder can range from about 1% to about 45% of the joint compound total wet weight. More preferably, the binder comprises from about 1% to about 20% of the total wet weight, and most preferably, from about 4% to about 14%. Preferred binders are Rhoplex HG 74M and Rhoplex AC 417M acrylic copolymers available from Rohm and Haas, Philadelphia, Pa.
A surfactant can also be included in the joint compound formulation, particularly when the dust reducing additive includes an oil. Certain surfactants have also been found to act as dust reducing additives by themselves. A preferred surfactant is Triton X-405, a nonionic surfactant available from Union Carbide Chemicals and Plastics Co. Inc., Danbury, Conn. The surfactant generally comprises less than about 3.5% of the joint compound total wet weight, and preferably less than about 0.25%.
Many joint compound formulations also contain a cellulosic thickener, usually a cellulosic ether. Suitable thickeners include methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxyethyl hydroxypropyl cellulose, ethylhydroxyethyl cellulose, and sodium carboxymethyl cellulose (CMC). These thickeners can be used alone or in combination with one another. The amount of cellulosic thickener can range from about 0.1% to about 2% by weight of the joint compound. A preferred thickener is hydroxypropyl methyl cellulose available from Dow Chemical Company under the trade designation Methocel.
Another ingredient that can be included in the joint compound of the invention is a non-leveling agent. Suitable non-leveling agents include clays such as attapulgus clay, bentonite, illite, kaolin and sepiolite, and clays mixed with starches. Thickeners, such as those described above, can also function as non-leveling agents.
To provide a lighter weight joint compound, glass bubbles or a specially treated expanded perlite can be added as described in U.S. Pat. No. 4,454,267. Additional ingredients which can be utilized in the joint compound are preservatives, fungicides, anti-freeze wetting agents, defoamers, flocculents, such as polyacrylamide resin, and plasticizers, such as dipropylene glycol dibenzoate.
In accordance with a characterizing feature of the present invention, the joint compound includes an ingredient which serves to minimize the quantity of airborne particles generated during sanding of the hardened joint compound. The additive generally comprises less than 20% of the joint compound total wet weight. More preferably, the dust reducing additive comprises between about 0.1% and about 10% of the joint compound by wet weight percent and, most preferably, between about 1.5% and about 6%.
Many ingredients have been found to effectively reduce the quantity of airborne particles generated when sanding the joint compound including oils such as animal, vegetable, and mineral oils (saturated and unsaturated), and oils derived from petroleum, pitch, natural and synthetic waxes, paraffins, solvents which evaporate slower than water, terpenes, glycols, surfactants, and mixtures thereof. A preferred dust reducing additive is a mixture of mineral oil and an unsaturated oil, such as corn oil, comprising from about 1.5% to about 6% of the joint compound total wet weight, and a surfactant comprising from about 0.15% to about 0.40% of the joint compound total wet weight. It has also been found that increasing the level of resin in the joint compound may serve to reduce the level of airborne dust generated during sanding.
While the manner by which each additive serves to suppress the formation of particles capable of becoming airborne is not fully understood, some general observations have been made. For example, it was observed that the joint compounds containing a dust reducing additive seemed to produce particles which were larger and heavier than the particles produced by joint compounds without a dust reducing additive. Thus, the dust reducing additive may cause the dust particles to agglomerate or stick together, thereby forming large heavy particles which tend not to become or remain airborne. The invention, however, is not intended to be limited to any particular mechanism.
The relative quantity of the various ingredients can vary substantially in accordance with the invention. Table 1 shows the general range of each ingredient for either a setting type joint compound or a ready-mixed type joint compound in its wet condition:
The teat procedure for measuring the quantity of airborne particles generated when sanding the hardened joint compound was as follows. First, each test specimen was prepared according to a specific formulation. The specific formulations for the various joint compounds are described more fully below along with the method used to prepare the specimens. The test specimens were approximately five inches long, one and one-half inches wide, and one quarter of an inch thick (5xe2x80x3 by 1xc2xdxe2x80x3 by xc2xcxe2x80x3). Before sanding, each test specimen was allowed to completely harden for at least twenty four hours at room temperature in an environment where the relative humidity generally ranged from about 25% to about 75%.
Referring to FIG. 1, there is shown the test enclosure 2 that was used to sand the test specimens 4a, 4b, 4c and measure the quantity of airborne dust particles generated. The enclosure 2 was a rectangular box six feet high, four feet wide, and two feet wide (6xe2x80x2xc3x974xe2x80x2xc3x972xe2x80x2). The top 6, bottom 8, side 10, and rear walls 12 of the enclosure 2 were constructed of wood, and the front wall 14 was constructed of transparent Plexiglas. A generally triangular access opening 16 located about one foot above the bottom wall 8 was provided in the front wall 14 to allow the individual conducting the test to insert his or her hand and arm into the enclosure and sand the specimen. The access opening 16 had a base dimension of about 7xc2xd inches and a height of about 8xc2xd inches. A movable cover member 18 was provided to allow the enclosure 2 to be completely sealed when sanding was completed. To sand the specimens 4a, 4b, 4c, the cover 18 was arranged in its up position as shown by the solid lines in FIG. 1. When sanding was completed, the cover 18 was pivoted downwardly to completely cover the access opening 16 as shown in phantom 18xe2x80x2.
As shown, three specimens 4a, 4b, 4c of joint compound were prepared on a section of wallboard 20 and the section of wallboard 20 was clamped to a mounting block 22 arranged within the enclosure 2. When tested, the specimens were located about twelve inches above the bottom wall 8 of the enclosure. Each specimen was tested individually and after each test, the enclosure was cleaned so that the quantity of airborne dust particles measured less than 0.05 mg/m3. A particle counter 24 for measuring the quantity of airborne particles was mounted in the right side wall about forty eight inches above the center of the specimens 4a, 4b, and 4c. 
The test specimens were sanded using a model B04552 power palm sander available from Makita Corporation of America, Buford, Ga. The sander included a 4xc2xdxc3x974 inch pad equipped with a 120 grit mesh sanding screen mounted over a 5xc3x973xc2xdxc3x97xc2xe inch open, semi-rigid, non-woven, heavy duty, stripping, backing pad available from Minnesota Mining and Manufacturing Company, St. Paul Minn. Sanding was performed at a sanding speed of approximately 14,000 OPM (orbits per minute) using ordinary sanding pressure. Ordinary sanding pressure is defined as the amount of pressure typically required to sand a hardened joint compound. Sanding pressure, therefore, is the manual pressure typically applied by an ordinary person when sanding a joint compound. It will be recognized that the sanding pressure can vary depending on the hardness of the joint compound. Sanding was continued until the specimen was completely sanded. That is, the entire thickness of the specimen was sanded so that a generally smooth wall surface was produced. Care was taken to ensure that sanding was discontinued before the drywall itself was sanded. The amount of time required to sand each specimen varied depending on the hardness of the joint compound and the sanding pressure.
The quantity of airborne dust particles was measured starting from the time sanding was initiated until several minutes after sanding was discontinued. In general, the level of airborne dust was measured until the level decreased to less than 50% of its peak level. The quantity of airborne dust was measured using a DUSTTRAK(trademark) aerosol monitor model 8520 available from TSI Incorporated, St. Paul, Minn. The particle counter measures the number of particles having a size of less than or equal to 10 microns. In the Examples, the peak or highest level of airborne dust measured during the test is presented.
A summary of the various ingredients used to prepare the joint compounds in each of the Examples is provided below:
Fillers
Calcium Carbonatexe2x80x94Marble Dust available from ECC International, Sylacauga, Ala.
Calcium Sulfate Dihydratexe2x80x94available from J. T. Baker Chemical Co., Phillipsburg, N.J.
Micaxe2x80x94Mica AMC available from Kraft Chemical Co., Melrose Park, Ill. Mica prevents cracks from forming as the joint compound hardens.
Kaolinxe2x80x94Aldrich Chemical Co., Milwaukee, Wis.
Glass Bubblesxe2x80x94K1 (177 microns-0.14 g/cm3) glass bubbles available from Minnesota Mining and Manufacturing Company, St. Paul, Minn. Glass bubbles improve the sandability of the joint compound and help to form a lighter weight joint compound.
Binders
Rhoplex HG 74M, Rhoplex HG 74P, Rhoplex AC 417M, Rhoplex 2620, and
Rhoplex EC-2848 xe2x80x94acrylic resins available from Rohm and Haas, Philadelphia, Pa.
Airflex RP-226 xe2x80x94vinyl acetate-ethylene copolymer available from Air Products and Chemicals, Inc., Allentown, Pa.
Waxes
Octowax 321 xe2x80x94available from Tiarco Chemical Div., Textile Robber and Chemical Co., Dalton, Ga.
Boler 1070 xe2x80x94a paraffin wax available from Boler Inc., Wayne Pa.
Carbowax 540 xe2x80x94synthetic wax available from Union Carbide Corp., Danbury, Conn.
Oils
Corn Oilxe2x80x94conventional corn oil. A suitable corn oil is available from Eastman Kodak Co., Rochester, N.Y.
Linoleic Acidxe2x80x94an unsaturated oil, available from Eastman Kodak Co., Rochester, N.Y.
Castor Oilxe2x80x94an unsaturated vegetable oil available from Aldrich Chemical Co., Milwaukee, Wis.
Tung Oilxe2x80x94an unsaturated vegetable oil available from Woodworkers Store, Medina, Minn.
Mineral Oilxe2x80x94Carnation light mineral oil available from Witco Corporation, Sonneborn Division, New York, N.Y.
Surfactants Surfactants were generally included in the joint compound formulations when the dust reducing additive included an oil to help emulsify the oil and combine it with a water based joint compound. Certain surfactants, however, were found to have a dust reducing effect when used by themselves.
FC 430 xe2x80x94a nonionic surfactant available from Minnesota Mining and Manufacturing Company, Industrial Chemicals, St. Paul, Minn.
Triton X-405 xe2x80x94a nonionic surfactant (octylphenoxy polyethoxy ethanol) available from Union Carbide Chemicals and Plastics Co. Inc., Danbury, Conn.
Variquat B-200 xe2x80x94a cationic surfactant (benzyl trimethyl ammonium chloride 60%) available from Sherex Chemical Co. Inc., Dublin, Ohio.
Steol KS 460 xe2x80x94an anionic surfactant (alkyl ether sulfate sodium salt 60%) available from Stephon Chemical Co., Northfield, Ill.
Span 85 xe2x80x94a nonionic surfactant (sorbitan trioleate) available from ICI Americas Inc., Wilmington, Del.
Tween 80 xe2x80x94nonionic surfactant (polysorbate 80) available from ICI Americas Inc., Wilmington, Del.
Solvents
Isopar Mxe2x80x94an aliphatic hydrocarbon available from Exxon Chemical Co., Houston, Tex.
Norpar 15 xe2x80x94a normal paraffin available from Exxon Chemical Co., Houston, Tex.
Heptanexe2x80x94available from Aldrich Chemical Co, Milwaukee, Wis.
Isopropanolxe2x80x94available from Aldrich Chemical Co, Milwaukee, Wis.
Propylene carbonatexe2x80x94available from Arco Chemical Co., Newton Square, Pa., under the trade designation Arconate HP.
Tripropylene glycol methyl ether available from Dow Chemical Co., Midland, Mich.
Tripropylene glycol-n-butyl ether available from Dow Chemical Co., Midland, Mich.
Ethylene glycol phenyl ether available from Dow Chemical Co., Midland, Mich.
D. Limonenexe2x80x94a terpene available from SCM Glidden Organics, Jacksonville, Fla.
Exxsol D-110 xe2x80x94an aliphatic hydrocarbon available from Exxon Chemical Co., Houston, Tex.
Exxate 1300 xe2x80x94C13 alkyl acetate available from Exxon Chemical Co., Houston, Tex.
Glycerolxe2x80x94available from J. T. Baker Chemical Co, Phillipsburg, N.J.
Thickener
Methocel 311 xe2x80x94hydroxypropyl methylcellulose available from Dow Chemical Co., Midland, Mich.